Enormous demands for energy storage devices have resulted in development of supercapacitor, especially for applications in electronic devices and hybrid vehicles. Carbon-based materials such as activated carbon and carbon nanotubes have been widely applied to Electrical Double Layer Capacitance (EDLC) supercapacitors.
Pseudocapacitors are also one of the existing types of supercapacitors. The pseudocapacitors have electrodes made up of metal oxide/hydroxides and conducting polymers and employ oxidation/reduction (redox) mechanism, which occurs within the electrode materials.
Recent developments in the domain of supercapacitors disclose use of graphene as a carbon material for use in fabrication of supercapacitors. The properties of graphene such as theoretically large surface area, excellent conductivity, good capacitance behavior, and low production cost make it a promising carbon material for supercapacitors. It has been evident by experimental exercises that graphene exhibits a very high electron mobility and a low resistivity, which are ideal for electrochemical storage devices.
Further, polypyrrole (PPy) is an attractive supercapacitor because of its excellent electrical and capacitance properties, good environmental stability, and ease of preparation. Further, PPy has an additional advantage of being used in flexible supercapacitors by virtue of its effective mechanical flexibility. The metal oxides MnO2, RuO2, and CoO have also been widely used as supercapacitor materials. In addition to aforesaid metal oxides, zinc oxide (ZnO) possesses a high energy density and is therefore highly suitable for supercapacitor applications. Further, it is also discovered that a ZnO/graphene nanocomposite exhibits excellent long-term charge/discharge recycling ability with a high capacitive performance.
US2013/0155579A1 titled “Flexible conducting polymer energy storage device” by Massachusetts Institute of Technology describes an electrochemical redox supercapacitor which consists of two thin films of electrically conducting polymer separated by an ion-permeable membrane and an electrolyte disposed between the two thin films. Further, a multi-step method is disclosed for manufacturing the redox supercapacitor.
US 2014/0087192A1 titled “Conducting polymer/graphene-based material composites, and methods for preparing the composites” by Agency for Science, Technology & Research and Nanyang Technological University discloses a composite comprising a conducting polymer and a graphene-based material is provided. The composite includes a graphene-based material doped with nitrogen or having a nitrogen-containing species grafted thereon, and a conducting polymer arranged on the graphene-based material. Further, the aforesaid document discloses a two-step method comprising doping graphene oxide with nitrogen followed by polymerization of monomers of the conducting polymer on the graphene-based materials in the presence of an oxidant to form the composite.
One of the major problems in existing supercapacitors is the weak cycling stability upon continual charge/discharge. Electrostatic storage mechanism of an EDLC-based electrode stores only limited charges. Further, the fabrication process of such supercapacitors is very complex and comprises of multiple steps.
Accordingly, there remains a need in the prior arts to have a flexible supercapacitor which overcomes the aforesaid problems and shortcomings.
However, there remains a need in the art for a flexible capacitor having excellent electrochemical, good mechanical strength, light weight, remarkable flexibility and simple fabrication process. Further, it should have the capability to withstand stress at various curvatures.